2 package Moose::Meta::Attribute;
7 use Scalar::Util 'blessed', 'weaken';
10 our $VERSION = '0.91';
11 our $AUTHORITY = 'cpan:STEVAN';
13 use Moose::Meta::Method::Accessor;
14 use Moose::Meta::Method::Delegation;
16 use Moose::Util::TypeConstraints ();
18 use base 'Class::MOP::Attribute';
20 # options which are not directly used
21 # but we store them for metadata purposes
22 __PACKAGE__->meta->add_attribute('isa' => (reader => '_isa_metadata'));
23 __PACKAGE__->meta->add_attribute('does' => (reader => '_does_metadata'));
24 __PACKAGE__->meta->add_attribute('is' => (reader => '_is_metadata'));
26 # these are actual options for the attrs
27 __PACKAGE__->meta->add_attribute('required' => (reader => 'is_required' ));
28 __PACKAGE__->meta->add_attribute('lazy' => (reader => 'is_lazy' ));
29 __PACKAGE__->meta->add_attribute('lazy_build' => (reader => 'is_lazy_build' ));
30 __PACKAGE__->meta->add_attribute('coerce' => (reader => 'should_coerce' ));
31 __PACKAGE__->meta->add_attribute('weak_ref' => (reader => 'is_weak_ref' ));
32 __PACKAGE__->meta->add_attribute('auto_deref' => (reader => 'should_auto_deref'));
33 __PACKAGE__->meta->add_attribute('type_constraint' => (
34 reader => 'type_constraint',
35 predicate => 'has_type_constraint',
37 __PACKAGE__->meta->add_attribute('trigger' => (
39 predicate => 'has_trigger',
41 __PACKAGE__->meta->add_attribute('handles' => (
43 writer => '_set_handles',
44 predicate => 'has_handles',
46 __PACKAGE__->meta->add_attribute('documentation' => (
47 reader => 'documentation',
48 predicate => 'has_documentation',
50 __PACKAGE__->meta->add_attribute('traits' => (
51 reader => 'applied_traits',
52 predicate => 'has_applied_traits',
55 # we need to have a ->does method in here to
56 # more easily support traits, and the introspection
57 # of those traits. We extend the does check to look
58 # for metatrait aliases.
60 my ($self, $role_name) = @_;
62 Moose::Util::resolve_metatrait_alias(Attribute => $role_name)
64 return 0 if !defined($name); # failed to load class
65 return $self->Moose::Object::does($name);
70 my $class = ( ref $self && $self->associated_class ) || "Moose::Meta::Class";
71 unshift @_, "message" if @_ % 2 == 1;
72 unshift @_, attr => $self if ref $self;
74 my $handler = $class->can("throw_error"); # to avoid incrementing depth by 1
79 my ($class, $name, %options) = @_;
80 $class->_process_options($name, \%options) unless $options{__hack_no_process_options}; # used from clone()... YECHKKK FIXME ICKY YUCK GROSS
82 delete $options{__hack_no_process_options};
87 map { $_->init_arg() }
88 $class->meta()->get_all_attributes()
91 my @bad = sort grep { ! $attrs{$_} } keys %options;
95 Carp::cluck "Found unknown argument(s) passed to '$name' attribute constructor in '$class': @bad";
98 return $class->SUPER::new($name, %options);
101 sub interpolate_class_and_new {
102 my ($class, $name, %args) = @_;
104 my ( $new_class, @traits ) = $class->interpolate_class(\%args);
106 $new_class->new($name, %args, ( scalar(@traits) ? ( traits => \@traits ) : () ) );
109 sub interpolate_class {
110 my ($class, $options) = @_;
112 $class = ref($class) || $class;
114 if ( my $metaclass_name = delete $options->{metaclass} ) {
115 my $new_class = Moose::Util::resolve_metaclass_alias( Attribute => $metaclass_name );
117 if ( $class ne $new_class ) {
118 if ( $new_class->can("interpolate_class") ) {
119 return $new_class->interpolate_class($options);
128 if (my $traits = $options->{traits}) {
130 while ($i < @$traits) {
131 my $trait = $traits->[$i++];
132 next if ref($trait); # options to a trait we discarded
134 $trait = Moose::Util::resolve_metatrait_alias(Attribute => $trait)
137 next if $class->does($trait);
139 push @traits, $trait;
142 push @traits, $traits->[$i++]
143 if $traits->[$i] && ref($traits->[$i]);
147 my $anon_class = Moose::Meta::Class->create_anon_class(
148 superclasses => [ $class ],
149 roles => [ @traits ],
153 $class = $anon_class->name;
157 return ( wantarray ? ( $class, @traits ) : $class );
162 my @legal_options_for_inheritance = qw(
163 default coerce required
164 documentation lazy handles
165 builder type_constraint
170 sub legal_options_for_inheritance { @legal_options_for_inheritance }
173 # This method *must* be able to handle
174 # Class::MOP::Attribute instances as
175 # well. Yes, I know that is wrong, but
176 # apparently we didn't realize it was
177 # doing that and now we have some code
178 # which is dependent on it. The real
179 # solution of course is to push this
180 # feature back up into Class::MOP::Attribute
181 # but I not right now, I am too lazy.
182 # However if you are reading this and
183 # looking for something to do,.. please
186 sub clone_and_inherit_options {
187 my ($self, %options) = @_;
194 # we may want to extends a Class::MOP::Attribute
195 # in which case we need to be able to use the
196 # core set of legal options that have always
197 # been here. But we allows Moose::Meta::Attribute
198 # instances to changes them.
200 my @legal_options = $self->can('legal_options_for_inheritance')
201 ? $self->legal_options_for_inheritance
202 : @legal_options_for_inheritance;
204 foreach my $legal_option (@legal_options) {
205 if (exists $options{$legal_option}) {
206 $actual_options{$legal_option} = $options{$legal_option};
207 delete $options{$legal_option};
213 if (blessed($options{isa}) && $options{isa}->isa('Moose::Meta::TypeConstraint')) {
214 $type_constraint = $options{isa};
217 $type_constraint = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options{isa});
218 (defined $type_constraint)
219 || $self->throw_error("Could not find the type constraint '" . $options{isa} . "'", data => $options{isa});
222 $actual_options{type_constraint} = $type_constraint;
223 delete $options{isa};
226 if ($options{does}) {
228 if (blessed($options{does}) && $options{does}->isa('Moose::Meta::TypeConstraint')) {
229 $type_constraint = $options{does};
232 $type_constraint = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options{does});
233 (defined $type_constraint)
234 || $self->throw_error("Could not find the type constraint '" . $options{does} . "'", data => $options{does});
237 $actual_options{type_constraint} = $type_constraint;
238 delete $options{does};
242 # this doesn't apply to Class::MOP::Attributes,
243 # so we can ignore it for them.
245 if ($self->can('interpolate_class')) {
246 ( $actual_options{metaclass}, my @traits ) = $self->interpolate_class(\%options);
249 my @all_traits = grep { $seen{$_}++ } @{ $self->applied_traits || [] }, @traits;
250 $actual_options{traits} = \@all_traits if @all_traits;
252 delete @options{qw(metaclass traits)};
255 (scalar keys %options == 0)
256 || $self->throw_error("Illegal inherited options => (" . (join ', ' => keys %options) . ")", data => \%options);
259 $self->clone(%actual_options);
263 my ( $self, %params ) = @_;
265 my $class = delete $params{metaclass} || ref $self;
267 my ( @init, @non_init );
269 foreach my $attr ( grep { $_->has_value($self) } Class::MOP::class_of($self)->get_all_attributes ) {
270 push @{ $attr->has_init_arg ? \@init : \@non_init }, $attr;
273 my %new_params = ( ( map { $_->init_arg => $_->get_value($self) } @init ), %params );
275 my $name = delete $new_params{name};
277 my $clone = $class->new($name, %new_params, __hack_no_process_options => 1 );
279 foreach my $attr ( @non_init ) {
280 $attr->set_value($clone, $attr->get_value($self));
286 sub _process_options {
287 my ($class, $name, $options) = @_;
289 if (exists $options->{is}) {
291 ### -------------------------
292 ## is => ro, writer => _foo # turns into (reader => foo, writer => _foo) as before
293 ## is => rw, writer => _foo # turns into (reader => foo, writer => _foo)
294 ## is => rw, accessor => _foo # turns into (accessor => _foo)
295 ## is => ro, accessor => _foo # error, accesor is rw
296 ### -------------------------
298 if ($options->{is} eq 'ro') {
299 $class->throw_error("Cannot define an accessor name on a read-only attribute, accessors are read/write", data => $options)
300 if exists $options->{accessor};
301 $options->{reader} ||= $name;
303 elsif ($options->{is} eq 'rw') {
304 if ($options->{writer}) {
305 $options->{reader} ||= $name;
308 $options->{accessor} ||= $name;
311 elsif ($options->{is} eq 'bare') {
312 # do nothing, but don't complain (later) about missing methods
315 $class->throw_error("I do not understand this option (is => " . $options->{is} . ") on attribute ($name)", data => $options->{is});
319 if (exists $options->{isa}) {
320 if (exists $options->{does}) {
321 if (eval { $options->{isa}->can('does') }) {
322 ($options->{isa}->does($options->{does}))
323 || $class->throw_error("Cannot have an isa option and a does option if the isa does not do the does on attribute ($name)", data => $options);
326 $class->throw_error("Cannot have an isa option which cannot ->does() on attribute ($name)", data => $options);
330 # allow for anon-subtypes here ...
331 if (blessed($options->{isa}) && $options->{isa}->isa('Moose::Meta::TypeConstraint')) {
332 $options->{type_constraint} = $options->{isa};
335 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options->{isa});
338 elsif (exists $options->{does}) {
339 # allow for anon-subtypes here ...
340 if (blessed($options->{does}) && $options->{does}->isa('Moose::Meta::TypeConstraint')) {
341 $options->{type_constraint} = $options->{does};
344 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options->{does});
348 if (exists $options->{coerce} && $options->{coerce}) {
349 (exists $options->{type_constraint})
350 || $class->throw_error("You cannot have coercion without specifying a type constraint on attribute ($name)", data => $options);
351 $class->throw_error("You cannot have a weak reference to a coerced value on attribute ($name)", data => $options)
352 if $options->{weak_ref};
355 if (exists $options->{trigger}) {
356 ('CODE' eq ref $options->{trigger})
357 || $class->throw_error("Trigger must be a CODE ref on attribute ($name)", data => $options->{trigger});
360 if (exists $options->{auto_deref} && $options->{auto_deref}) {
361 (exists $options->{type_constraint})
362 || $class->throw_error("You cannot auto-dereference without specifying a type constraint on attribute ($name)", data => $options);
363 ($options->{type_constraint}->is_a_type_of('ArrayRef') ||
364 $options->{type_constraint}->is_a_type_of('HashRef'))
365 || $class->throw_error("You cannot auto-dereference anything other than a ArrayRef or HashRef on attribute ($name)", data => $options);
368 if (exists $options->{lazy_build} && $options->{lazy_build} == 1) {
369 $class->throw_error("You can not use lazy_build and default for the same attribute ($name)", data => $options)
370 if exists $options->{default};
371 $options->{lazy} = 1;
372 $options->{builder} ||= "_build_${name}";
374 $options->{clearer} ||= "_clear${name}";
375 $options->{predicate} ||= "_has${name}";
378 $options->{clearer} ||= "clear_${name}";
379 $options->{predicate} ||= "has_${name}";
383 if (exists $options->{lazy} && $options->{lazy}) {
384 (exists $options->{default} || defined $options->{builder} )
385 || $class->throw_error("You cannot have lazy attribute ($name) without specifying a default value for it", data => $options);
388 if ( $options->{required} && !( ( !exists $options->{init_arg} || defined $options->{init_arg} ) || exists $options->{default} || defined $options->{builder} ) ) {
389 $class->throw_error("You cannot have a required attribute ($name) without a default, builder, or an init_arg", data => $options);
394 sub initialize_instance_slot {
395 my ($self, $meta_instance, $instance, $params) = @_;
396 my $init_arg = $self->init_arg();
397 # try to fetch the init arg from the %params ...
401 if ( defined($init_arg) and exists $params->{$init_arg}) {
402 $val = $params->{$init_arg};
406 # skip it if it's lazy
407 return if $self->is_lazy;
408 # and die if it's required and doesn't have a default value
409 $self->throw_error("Attribute (" . $self->name . ") is required", object => $instance, data => $params)
410 if $self->is_required && !$self->has_default && !$self->has_builder;
412 # if nothing was in the %params, we can use the
413 # attribute's default value (if it has one)
414 if ($self->has_default) {
415 $val = $self->default($instance);
418 elsif ($self->has_builder) {
419 $val = $self->_call_builder($instance);
424 return unless $value_is_set;
426 $val = $self->_coerce_and_verify( $val, $instance );
428 $self->set_initial_value($instance, $val);
430 if ( ref $val && $self->is_weak_ref ) {
431 $self->weaken_value($instance);
436 my ( $self, $instance ) = @_;
438 my $builder = $self->builder();
440 return $instance->$builder()
441 if $instance->can( $self->builder );
443 $self->throw_error( blessed($instance)
444 . " does not support builder method '"
446 . "' for attribute '"
456 # this duplicates too much code from
457 # Class::MOP::Attribute, we need to
458 # refactor these bits eventually.
460 sub _set_initial_slot_value {
461 my ($self, $meta_instance, $instance, $value) = @_;
463 my $slot_name = $self->name;
465 return $meta_instance->set_slot_value($instance, $slot_name, $value)
466 unless $self->has_initializer;
468 my ($type_constraint, $can_coerce);
469 if ($self->has_type_constraint) {
470 $type_constraint = $self->type_constraint;
471 $can_coerce = ($self->should_coerce && $type_constraint->has_coercion);
475 my $val = $self->_coerce_and_verify( shift, $instance );;
477 $meta_instance->set_slot_value($instance, $slot_name, $val);
480 my $initializer = $self->initializer;
482 # most things will just want to set a value, so make it first arg
483 $instance->$initializer($value, $callback, $self);
487 my ($self, $instance, @args) = @_;
488 my $value = $args[0];
490 my $attr_name = $self->name;
492 if ($self->is_required and not @args) {
493 $self->throw_error("Attribute ($attr_name) is required", object => $instance);
496 $value = $self->_coerce_and_verify( $value, $instance );
499 if ( $self->has_trigger && $self->has_value($instance) ) {
500 @old = $self->get_value($instance, 'for trigger');
503 $self->SUPER::set_value($instance, $value);
505 if ( ref $value && $self->is_weak_ref ) {
506 $self->weaken_value($instance);
509 if ($self->has_trigger) {
510 $self->trigger->($instance, $value, @old);
515 my ( $self, $instance ) = @_;
518 Class::MOP::Class->initialize( blessed($instance) )->get_meta_instance;
520 $meta_instance->weaken_slot_value( $instance, $self->name );
524 my ($self, $instance, $for_trigger) = @_;
526 if ($self->is_lazy) {
527 unless ($self->has_value($instance)) {
529 if ($self->has_default) {
530 $value = $self->default($instance);
531 } elsif ( $self->has_builder ) {
532 $value = $self->_call_builder($instance);
535 $value = $self->_coerce_and_verify( $value, $instance );
537 $self->set_initial_value($instance, $value);
541 if ( $self->should_auto_deref && ! $for_trigger ) {
543 my $type_constraint = $self->type_constraint;
545 if ($type_constraint->is_a_type_of('ArrayRef')) {
546 my $rv = $self->SUPER::get_value($instance);
547 return unless defined $rv;
548 return wantarray ? @{ $rv } : $rv;
550 elsif ($type_constraint->is_a_type_of('HashRef')) {
551 my $rv = $self->SUPER::get_value($instance);
552 return unless defined $rv;
553 return wantarray ? %{ $rv } : $rv;
556 $self->throw_error("Can not auto de-reference the type constraint '" . $type_constraint->name . "'", object => $instance, type_constraint => $type_constraint);
562 return $self->SUPER::get_value($instance);
566 ## installing accessors
568 sub accessor_metaclass { 'Moose::Meta::Method::Accessor' }
570 sub install_accessors {
572 $self->SUPER::install_accessors(@_);
573 $self->install_delegation if $self->has_handles;
577 sub _check_associated_methods {
580 @{ $self->associated_methods }
581 || ($self->_is_metadata || '') eq 'bare'
584 'Attribute (' . $self->name . ') of class '
585 . $self->associated_class->name
586 . ' has no associated methods'
587 . ' (did you mean to provide an "is" argument?)'
593 sub _process_accessors {
595 my ($type, $accessor, $generate_as_inline_methods) = @_;
596 $accessor = (keys %$accessor)[0] if (ref($accessor)||'') eq 'HASH';
597 my $method = $self->associated_class->get_method($accessor);
598 if ($method && !$method->isa('Class::MOP::Method::Accessor')
599 && (!$self->definition_context
600 || $method->package_name eq $self->definition_context->{package})) {
602 "You are overwriting a locally defined method ($accessor) with "
606 $self->SUPER::_process_accessors(@_);
609 sub remove_accessors {
611 $self->SUPER::remove_accessors(@_);
612 $self->remove_delegation if $self->has_handles;
616 sub install_delegation {
620 # Here we canonicalize the 'handles' option
621 # this will sort out any details and always
622 # return an hash of methods which we want
623 # to delagate to, see that method for details
624 my %handles = $self->_canonicalize_handles;
627 # install the delegation ...
628 my $associated_class = $self->associated_class;
629 foreach my $handle (keys %handles) {
630 my $method_to_call = $handles{$handle};
631 my $class_name = $associated_class->name;
632 my $name = "${class_name}::${handle}";
634 (!$associated_class->has_method($handle))
635 || $self->throw_error("You cannot overwrite a locally defined method ($handle) with a delegation", method_name => $handle);
638 # handles is not allowed to delegate
639 # any of these methods, as they will
640 # override the ones in your class, which
641 # is almost certainly not what you want.
643 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
644 #cluck("Not delegating method '$handle' because it is a core method") and
645 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
647 my $method = $self->_make_delegation_method($handle, $method_to_call);
649 $self->associated_class->add_method($method->name, $method);
650 $self->associate_method($method);
654 sub remove_delegation {
656 my %handles = $self->_canonicalize_handles;
657 my $associated_class = $self->associated_class;
658 foreach my $handle (keys %handles) {
659 $self->associated_class->remove_method($handle);
663 # private methods to help delegation ...
665 sub _canonicalize_handles {
667 my $handles = $self->handles;
668 if (my $handle_type = ref($handles)) {
669 if ($handle_type eq 'HASH') {
672 elsif ($handle_type eq 'ARRAY') {
673 return map { $_ => $_ } @{$handles};
675 elsif ($handle_type eq 'Regexp') {
676 ($self->has_type_constraint)
677 || $self->throw_error("Cannot delegate methods based on a Regexp without a type constraint (isa)", data => $handles);
678 return map { ($_ => $_) }
679 grep { /$handles/ } $self->_get_delegate_method_list;
681 elsif ($handle_type eq 'CODE') {
682 return $handles->($self, $self->_find_delegate_metaclass);
684 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::DuckType')) {
685 return map { $_ => $_ } @{ $handles->methods };
688 $self->throw_error("Unable to canonicalize the 'handles' option with $handles", data => $handles);
692 Class::MOP::load_class($handles);
693 my $role_meta = Class::MOP::class_of($handles);
695 (blessed $role_meta && $role_meta->isa('Moose::Meta::Role'))
696 || $self->throw_error("Unable to canonicalize the 'handles' option with $handles because its metaclass is not a Moose::Meta::Role", data => $handles);
698 return map { $_ => $_ }
699 grep { $_ ne 'meta' } (
700 $role_meta->get_method_list,
701 map { $_->name } $role_meta->get_required_method_list,
706 sub _find_delegate_metaclass {
708 if (my $class = $self->_isa_metadata) {
709 # we might be dealing with a non-Moose class,
710 # and need to make our own metaclass. if there's
711 # already a metaclass, it will be returned
712 return Moose::Meta::Class->initialize($class);
714 elsif (my $role = $self->_does_metadata) {
715 return Class::MOP::class_of($role);
718 $self->throw_error("Cannot find delegate metaclass for attribute " . $self->name);
722 sub _get_delegate_method_list {
724 my $meta = $self->_find_delegate_metaclass;
725 if ($meta->isa('Class::MOP::Class')) {
726 return map { $_->name } # NOTE: !never! delegate &meta
727 grep { $_->package_name ne 'Moose::Object' && $_->name ne 'meta' }
728 $meta->get_all_methods;
730 elsif ($meta->isa('Moose::Meta::Role')) {
731 return $meta->get_method_list;
734 $self->throw_error("Unable to recognize the delegate metaclass '$meta'", data => $meta);
738 sub delegation_metaclass { 'Moose::Meta::Method::Delegation' }
740 sub _make_delegation_method {
741 my ( $self, $handle_name, $method_to_call ) = @_;
745 $method_body = $method_to_call
746 if 'CODE' eq ref($method_to_call);
748 my @curried_arguments;
750 ($method_to_call, @curried_arguments) = @$method_to_call
751 if 'ARRAY' eq ref($method_to_call);
753 return $self->delegation_metaclass->new(
754 name => $handle_name,
755 package_name => $self->associated_class->name,
757 delegate_to_method => $method_to_call,
758 curried_arguments => \@curried_arguments,
762 sub _coerce_and_verify {
765 my $instance = shift;
767 return $val unless $self->has_type_constraint;
769 my $type_constraint = $self->type_constraint;
770 if ($self->should_coerce && $type_constraint->has_coercion) {
771 $val = $type_constraint->coerce($val);
774 $self->verify_against_type_constraint($val, instance => $instance);
779 sub verify_against_type_constraint {
783 return 1 if !$self->has_type_constraint;
785 my $type_constraint = $self->type_constraint;
787 $type_constraint->check($val)
788 || $self->throw_error("Attribute ("
790 . ") does not pass the type constraint because: "
791 . $type_constraint->get_message($val), data => $val, @_);
794 package Moose::Meta::Attribute::Custom::Moose;
795 sub register_implementation { 'Moose::Meta::Attribute' }
805 Moose::Meta::Attribute - The Moose attribute metaclass
809 This class is a subclass of L<Class::MOP::Attribute> that provides
810 additional Moose-specific functionality.
812 To really understand this class, you will need to start with the
813 L<Class::MOP::Attribute> documentation. This class can be understood
814 as a set of additional features on top of the basic feature provided
815 by that parent class.
819 C<Moose::Meta::Attribute> is a subclass of L<Class::MOP::Attribute>.
823 Many of the documented below override methods in
824 L<Class::MOP::Attribute> and add Moose specific features.
830 =item B<< Moose::Meta::Attribute->new(%options) >>
832 This method overrides the L<Class::MOP::Attribute> constructor.
834 Many of the options below are described in more detail in the
835 L<Moose::Manual::Attributes> document.
837 It adds the following options to the constructor:
841 =item * is => 'ro', 'rw', 'bare'
843 This provides a shorthand for specifying the C<reader>, C<writer>, or
844 C<accessor> names. If the attribute is read-only ('ro') then it will
845 have a C<reader> method with the same attribute as the name.
847 If it is read-write ('rw') then it will have an C<accessor> method
848 with the same name. If you provide an explicit C<writer> for a
849 read-write attribute, then you will have a C<reader> with the same
850 name as the attribute, and a C<writer> with the name you provided.
852 Use 'bare' when you are deliberately not installing any methods
853 (accessor, reader, etc.) associated with this attribute; otherwise,
854 Moose will issue a deprecation warning when this attribute is added to a
859 This option accepts a type. The type can be a string, which should be
860 a type name. If the type name is unknown, it is assumed to be a class
863 This option can also accept a L<Moose::Meta::TypeConstraint> object.
865 If you I<also> provide a C<does> option, then your C<isa> option must
866 be a class name, and that class must do the role specified with
869 =item * does => $role
871 This is short-hand for saying that the attribute's type must be an
872 object which does the named role.
874 =item * coerce => $bool
876 This option is only valid for objects with a type constraint
877 (C<isa>). If this is true, then coercions will be applied whenever
878 this attribute is set.
880 You can make both this and the C<weak_ref> option true.
882 =item * trigger => $sub
884 This option accepts a subroutine reference, which will be called after
885 the attribute is set.
887 =item * required => $bool
889 An attribute which is required must be provided to the constructor. An
890 attribute which is required can also have a C<default> or C<builder>,
891 which will satisfy its required-ness.
893 A required attribute must have a C<default>, C<builder> or a
894 non-C<undef> C<init_arg>
896 =item * lazy => $bool
898 A lazy attribute must have a C<default> or C<builder>. When an
899 attribute is lazy, the default value will not be calculated until the
902 =item * weak_ref => $bool
904 If this is true, the attribute's value will be stored as a weak
907 =item * auto_deref => $bool
909 If this is true, then the reader will dereference the value when it is
910 called. The attribute must have a type constraint which defines the
911 attribute as an array or hash reference.
913 =item * lazy_build => $bool
915 Setting this to true makes the attribute lazy and provides a number of
923 is equivalent to this:
928 builder => '_build_size',
929 clearer => 'clear_size',
930 predicate => 'has_size',
933 =item * documentation
935 An arbitrary string that can be retrieved later by calling C<<
936 $attr->documentation >>.
940 =item B<< $attr->clone(%options) >>
942 This creates a new attribute based on attribute being cloned. You must
943 supply a C<name> option to provide a new name for the attribute.
945 The C<%options> can only specify options handled by
946 L<Class::MOP::Attribute>.
950 =head2 Value management
954 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
956 This method is used internally to initialize the attribute's slot in
957 the object C<$instance>.
959 This overrides the L<Class::MOP::Attribute> method to handle lazy
960 attributes, weak references, and type constraints.
966 eval { $point->meta->get_attribute('x')->set_value($point, 'forty-two') };
971 I<Attribute (x) does not pass the type constraint (Int) with 'forty-two'>
973 Before setting the value, a check is made on the type constraint of
974 the attribute, if it has one, to see if the value passes it. If the
975 value fails to pass, the set operation dies with a L<throw_error>.
977 Any coercion to convert values is done before checking the type constraint.
979 To check a value against a type constraint before setting it, fetch the
980 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
981 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
982 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::Basics::Recipe4>
987 =head2 Attribute Accessor generation
991 =item B<< $attr->install_accessors >>
993 This method overrides the parent to also install delegation methods.
995 If, after installing all methods, the attribute object has no associated
996 methods, it throws an error unless C<< is => 'bare' >> was passed to the
997 attribute constructor. (Trying to add an attribute that has no associated
998 methods is almost always an error.)
1000 =item B<< $attr->remove_accessors >>
1002 This method overrides the parent to also remove delegation methods.
1004 =item B<< $attr->install_delegation >>
1006 This method adds its delegation methods to the attribute's associated
1007 class, if it has any to add.
1009 =item B<< $attr->remove_delegation >>
1011 This method remove its delegation methods from the attribute's
1014 =item B<< $attr->accessor_metaclass >>
1016 Returns the accessor metaclass name, which defaults to
1017 L<Moose::Meta::Method::Accessor>.
1019 =item B<< $attr->delegation_metaclass >>
1021 Returns the delegation metaclass name, which defaults to
1022 L<Moose::Meta::Method::Delegation>.
1026 =head2 Additional Moose features
1028 These methods are not found in the superclass. They support features
1033 =item B<< $attr->does($role) >>
1035 This indicates whether the I<attribute itself> does the given
1036 role. The role can be given as a full class name, or as a resolvable
1039 Note that this checks the attribute itself, not its type constraint,
1040 so it is checking the attribute's metaclass and any traits applied to
1043 =item B<< Moose::Meta::Class->interpolate_class_and_new($name, %options) >>
1045 This is an alternate constructor that handles the C<metaclass> and
1048 Effectively, this method is a factory that finds or creates the
1049 appropriate class for the given C<metaclass> and/or C<traits>.
1051 Once it has the appropriate class, it will call C<< $class->new($name,
1052 %options) >> on that class.
1054 =item B<< $attr->clone_and_inherit_options(%options) >>
1056 This method supports the C<has '+foo'> feature. It does various bits
1057 of processing on the supplied C<%options> before ultimately calling
1058 the C<clone> method.
1060 One of its main tasks is to make sure that the C<%options> provided
1061 only includes the options returned by the
1062 C<legal_options_for_inheritance> method.
1064 =item B<< $attr->legal_options_for_inheritance >>
1066 This returns a whitelist of options that can be overridden in a
1067 subclass's attribute definition.
1069 This exists to allow a custom metaclass to change or add to the list
1070 of options which can be changed.
1072 =item B<< $attr->type_constraint >>
1074 Returns the L<Moose::Meta::TypeConstraint> object for this attribute,
1077 =item B<< $attr->has_type_constraint >>
1079 Returns true if this attribute has a type constraint.
1081 =item B<< $attr->verify_against_type_constraint($value) >>
1083 Given a value, this method returns true if the value is valid for the
1084 attribute's type constraint. If the value is not valid, it throws an
1087 =item B<< $attr->handles >>
1089 This returns the value of the C<handles> option passed to the
1092 =item B<< $attr->has_handles >>
1094 Returns true if this attribute performs delegation.
1096 =item B<< $attr->is_weak_ref >>
1098 Returns true if this attribute stores its value as a weak reference.
1100 =item B<< $attr->is_required >>
1102 Returns true if this attribute is required to have a value.
1104 =item B<< $attr->is_lazy >>
1106 Returns true if this attribute is lazy.
1108 =item B<< $attr->is_lazy_build >>
1110 Returns true if the C<lazy_build> option was true when passed to the
1113 =item B<< $attr->should_coerce >>
1115 Returns true if the C<coerce> option passed to the constructor was
1118 =item B<< $attr->should_auto_deref >>
1120 Returns true if the C<auto_deref> option passed to the constructor was
1123 =item B<< $attr->trigger >>
1125 This is the subroutine reference that was in the C<trigger> option
1126 passed to the constructor, if any.
1128 =item B<< $attr->has_trigger >>
1130 Returns true if this attribute has a trigger set.
1132 =item B<< $attr->documentation >>
1134 Returns the value that was in the C<documentation> option passed to
1135 the constructor, if any.
1137 =item B<< $attr->has_documentation >>
1139 Returns true if this attribute has any documentation.
1141 =item B<< $attr->applied_traits >>
1143 This returns an array reference of all the traits which were applied
1144 to this attribute. If none were applied, this returns C<undef>.
1146 =item B<< $attr->has_applied_traits >>
1148 Returns true if this attribute has any traits applied.
1154 All complex software has bugs lurking in it, and this module is no
1155 exception. If you find a bug please either email me, or add the bug
1160 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1162 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1164 =head1 COPYRIGHT AND LICENSE
1166 Copyright 2006-2009 by Infinity Interactive, Inc.
1168 L<http://www.iinteractive.com>
1170 This library is free software; you can redistribute it and/or modify
1171 it under the same terms as Perl itself.